inspection: use pep517.meta.build from shell

With change we execute pep517 metadata build from within a new venv
retaining old `python setup.py egg_info` behaviour. We fallback to the
old behaviour if pep517 metadata build fails.

poetry/inspection/info.py

@@ -1,5 +1,6 @@
 import glob
 import logging
+import os
 import subprocess
 import tarfile
 import zipfile
@@ -12,8 +13,6 @@
 
 import pkginfo
 
-from pep517.build import compat_system as pep517_compat_system
-from pep517.meta import build as pep517_metadata_build
 from poetry.core.factory import Factory
 from poetry.core.packages import Package
 from poetry.core.packages import ProjectPackage
@@ -23,12 +22,24 @@
 from poetry.core.utils.helpers import parse_requires
 from poetry.core.utils.helpers import temporary_directory
 from poetry.core.version.markers import InvalidMarker
+from poetry.utils.env import EnvCommandError
+from poetry.utils.env import EnvManager
+from poetry.utils.env import VirtualEnv
 from poetry.utils.setup_reader import SetupReader
 from poetry.utils.toml_file import TomlFile
 
 
 logger = logging.getLogger(__name__)
 
+PEP517_MEATA_BUILD = """\
+import pep517.build
+import pep517.meta
+
+path='{source}'
+system=pep517.build.compat_system(path)
+pep517.meta.build(source_dir=path, dest='{dest}', system=system)
+"""
+
 
 class PackageInfoError(ValueError):
     def __init__(self, path):  # type: (Union[Path, str]) -> None
@@ -255,6 +266,10 @@ def _from_sdist_file(cls, path):  # type: (Path) -> PackageInfo
 
         return info.update(new_info)
 
+    @staticmethod
+    def has_setup_files(path):  # type: (Path) -> bool
+        return any((path / f).exists() for f in SetupReader.FILES)
+
     @classmethod
     def from_setup_files(cls, path):  # type: (Path) -> PackageInfo
         """
@@ -264,7 +279,7 @@ def from_setup_files(cls, path):  # type: (Path) -> PackageInfo
 
         :param path: Path to `setup.py` file
         """
-        if not any((path / f).exists() for f in SetupReader.FILES):
+        if not cls.has_setup_files(path):
             raise PackageInfoError(path)
 
         try:
@@ -416,13 +431,39 @@ def _pep517_metadata(cls, path):  # type (Path) -> PackageInfo
         except PackageInfoError:
             pass
 
+        cwd = Path.cwd()
+        os.chdir(path.as_posix())
+
         try:
             with temporary_directory() as tmp_dir:
-                pep517_metadata_build(
-                    source_dir=path.as_posix(),
-                    dest=tmp_dir,
-                    system=pep517_compat_system(source_dir=path.as_posix()),
-                )
+                EnvManager.build_venv(tmp_dir)
+                venv = VirtualEnv(Path(tmp_dir), Path(tmp_dir))
+
+                try:
+                    venv.run_pip(
+                        "install",
+                        "--disable-pip-version-check",
+                        "--no-deps",
+                        "pep517===0.8.2",
+                        "toml==0.10.1",
+                    )
+                    venv.run(
+                        "python",
+                        "-c",
+                        PEP517_MEATA_BUILD.format(source=path.as_posix(), dest=tmp_dir),
+                    )
+                except EnvCommandError:
+                    # something went wrong while attempting pep517 metadata build
+                    # fallback to egg_info if setup.py available
+                    setup_py = path / "setup.py"
+                    if not setup_py.exists():
+                        raise PackageInfoError(path)
+
+                    try:
+                        venv.run("python", "setup.py", "egg_info")
+                    except EnvCommandError:
+                        raise PackageInfoError(path)
+
                 return cls.from_metadata(Path(tmp_dir))
         except subprocess.CalledProcessError:
             cls._log("PEP 517 metadata build failed for {}".format(path), "debug")
@@ -431,6 +472,8 @@ def _pep517_metadata(cls, path):  # type (Path) -> PackageInfo
                     "Falling back to parsed setup.py file for {}".format(path), "debug"
                 )
                 return info
+        finally:
+            os.chdir(cwd.as_posix())
 
         # if we reach here, everything has failed and all hope is lost
         raise PackageInfoError(path)

pyproject.toml

@@ -60,7 +60,6 @@ keyring = [
 # Use subprocess32 for Python 2.7
 subprocess32 = { version = "^3.5", python = "~2.7" }
 importlib-metadata = {version = "^1.6.0", python = "<3.8"}
-pep517 = "^0.8.2"
 
 [tool.poetry.dev-dependencies]
 pytest = [